1. Field of the Invention
This invention relates to a material for electric contacts having arc-quenching properties, which material comprises an cured polymeric composition containing a metal powder filler.
2. Description of the Prior Art
Such material is described in U.S. Pat. No. 4,011,426. The materials described in that printed publication contain a metal powder consisting, e.g., of nickel, an electrically non-conducting powder, such as quartz powder, alumina powder or dolomite powder, and a plastic material which releases gases under the action of an electric arc, particularly a plastic material which releases electronegative gases under the action of an electric arc, such as polytetrafluoroethylene. The above-mentioned components of the contact material are held together by a binder. The binders which have been mentioned include thermoset plastics, such as phenol resins, urea resins, melamine resins, and particularly a multicomponent epoxy resin. If an epoxy resin is used, the known materials are made in that the powder components are stirred into a liquid to pastelike resin composition, which in addition to the basic epoxy resin contains a solvent and a hardening agent for curing (crosslinking) the synthetic resin.
Said known materials for electric contacts have not proved satisfactory in switching practice. If the metal powder content is so high that a specific electrical conductivity of at least 0.1 MS/m can be achieved, the burn-off during switching operations will be excessive and the arc-quenching activity will be inadequate. If the metal powder content is reduced in favor of the substances having arc-quenching properties so that an adequate arc-quenching activity is obtained, then the electric conductivity will not be sufficient for a conduction of the cut-off current during the arc-quenching time and the burn-off during switching operations will still be high.